1. Field of the Invention
This invention relates to an information signal recording and/or reproducing apparatus and more particularly to an apparatus arranged to record and/or reproduce a main information signal, in or from each of a plurality of areas extending in the longitudinal direction of a tape shaped recording medium.
1. Description of the Prior Art
It has recently become a trend in the field of magnetic recording in general to increase the density of recording. Video tape recorders (hereinafter referred to as VTR) are of no exception and have come to be arranged to perform magnetic recording in increased density with the tape allowed to travel at a lower speed. However, the conventional use of a fixed head for audio signal recording deteriorates the reproduced sound quality as it is impossible to have a sufficiently high relative speed with the fixed head. In a method contrived for the solution of this problem, the length of recording tracks to be formed with a rotary head is arranged to be longer than the conventional length to give room for recording audio signals one after another.
FIG. 1 of the accompanying drawings shows the tape transport system of a VTR which is arranged according to the above-stated prior art method. FIG. 2 shows the recording tracks formed on a magnetic tape by the VTR of FIG. 1. These illustrations include a magnetic tape 1 (hereinafter referred to as the tape); a rotary cylinder 2; magnetic heads 3 and 4 (hereinafter referred to as heads) which are mounted on the cylinder 2 at a phase difference of 180.degree. degrees and are arranged to have different azimuth angles from each other; video signal recording areas 5 of recording tracks formed on the tape 1; and audio signal recording areas which are also formed in these tracks. The video area 5 is a part of the track traced by the heads 3 and 4 with the rotary cylinder 2 turned 180.degree. degrees. The audio area 6 is a part of the track traced by the heads 3 and 4 with the rotary cylinder 2 turned to a degree .theta..degree.. With an audio signal which is PCM processed and time-base compressed recorded in the audio area 6 in the above-stated manner, it can be reproduced in a fairly high sound quality favorably comparing with the sound quality of an analog signal recorded and reproduced by an audio dedicated apparatus.
Meanwhile, there has been proposed another method, in which a VTR is arranged to record another audio signal also in the video area 5. According to this method, with the angle .theta. for one area assumed to be 36 degrees, five more areas which are similar to the audio area 6 are obtainable within the turning degree of 180.degree. of the rotary head in addition to the audio area 6. Then, with audio signals which are separately time-base compressed allowed to be respectively recorded in these areas, the VTR can be arranged to serve as an audio dedicated tape recorder which is capable of recording audio signals in six channels. The following is a brief description of this tape recorder:
The tape transport system of the tape recorder mentioned above is arranged as shown in FIG. 3. Recording tracks formed on the tape by this tape recorder are as shown in FIG. 4. In these drawings, the same parts as those shown in FIGS. 1 and 2 are indicated by the same reference numerals. Referring to FIG. 4, while the head 3 or 4 is tracing the tape from a point A to a point B, from the point B to a point C, from the point C to a point D, from the point D to a point E, from the point E to a point F and from the point F to another point G as shown in FIG. 3, the audio signals are recorded in areas CH1 to CH6. Each of these areas is usable for recording an audio signal separately from another. Each of these areas is also arranged to have the so-called azimuth overlapped writing performed thereon. However, the recording tracks within each of the areas CH1 to CH6 do not have to be on one and the same straight line. Further, a tracking control pilot signal is recorded in each area. However, these pilot signals are recorded in these areas without any correlation with each other.
In the case of this tape recorder (hereinafter referred to as a multi-channel tape recorder), recording and reproduction can be performed either solely in the forward travelling direction of the tape (for example, in the direction of arrow 7 of FIG. 3) or, if so desired, alternately in opposite directions. For example, referring to FIG. 4, recording or reproduction is performed in or from the areas CH1 to CH3 while the tape is allowed to travel in the direction of arrow 7 and in or from the areas CH4 to CH6 while the tape is travelling in the direction of arrow 9. In that instance, the inclination of the tracks in the areas CH1 to CH3 somewhat differs from that of the tracks formed in the areas CH4 to CH6. However, the difference between the two directions in the relative speed presents no problem as the travelling speed of the tape 1 is extremely low as compared with the turning speed of the heads 3 and 4.
FIGS. 5(a) to 5(j) show in a time chart the recording and reproducing operations of the tape recorder described above. FIG. 5(a) shows a phase detection pulse signal (hereinafter referred to as a signal PG(a)) which is produced in synchronism with the rotation of the rotary cylinder 2 in the form of a rectangular wave form of 30 Hz alternately repeating a high level and a low level (hereinafter referred to as H and L levels respectively) in a cycle of 1/60 sec. FIG. 5(b) shows a pulse signal (hereinafter referred to as a signal PG(b)) of the polarity opposite to that of the signal PG(a). The signal PG(a) remains at an H level while the head 3 turns from the point B to the point G of FIG. 3. The PG(b) signal remains at an H level while the head 4 turns from the point B to the point G.
FIG. 5(c) shows a data reading pulse signal obtained from the PG(a) signal. This signal (c) is used for sampling, for every other field, an audio signal produced during a period corresponding to one field (1/60 sec.) portion of a video signal. FIG. 5(d) shows a signal which is produced at an H level representing a signal processing period for adding the sampled one field portion of the audio signal or data as an error correcting redundant code by means of a RAM or the like or for changing the arrangement of data. FIG. 5(e) shows a signal which is produced at an H level to indicate a data recording period and to show a timing for recording on the tape the data obtained through the above-stated signal processing operation. The temporally flow of signals of FIGS. 5(a)-5(j) are as follows: The data is sampled during a period between points of time t1 and t3 (while the head 3 is shifting from the point B to the point G). The sampled data is subjected to the signal processing operation during a period between points of time t3 and t5 (while the head 3 is shifting from the point G to the point A) and is then recorded during a period between points of time t5 and t6 (or while the head 3 shifts from the point A to the point B). More specifically, the sampled data is recorded into the area CH1 of FIG. 4 by means of the head 3. Meanwhile, the data which is sampled while the signal PG(b) is at an H level is also subjected to the signal processing operation at a similar timing and is recorded into the area CH1 by the other head 4.
FIG. 5(f) shows a signal (hereinafter referred to as a signal PG(f)) which is obtained by phase shifting the signal PG(a) to a predetermined extent (or 36 degrees corresponding to one area). In case that an audio signal is to be recorded by using this signal PG(f) and another signal which is of the polarity opposite to that of the signal PG(f), the apparatus operates as follows: The data sampled during a period between points of time t2 and t4 is signal processed according to a signal shown at FIG. 5(g) and is recorded during a period between points of time t6 and t7 according to a signal shown at FIG. 5(h). In other words, the data is recorded in the area CH2 shown in FIG. 4 by the head 3 while the head 3 is tracing the tape from a point B to another point C. The data which is sampled during points of time t4 and t7 is likewise recorded in the area CH2 by the head 4.
During the period between the points of time t6 and t7 (or between t1 and t2), the signal recorded in the area CH2 is reproduced in the following manner: The head 3 reads data from the tape 1 according to the signal of FIG. 5(h). The data which is thus read is signal processed according to a signal shown at FIG. 5(i) during a period between points of time t7 and t8 (or between t2 and t3) in a manner reverse to the signal processing operation performed during recording. Error correction, etc. are accomplished during this period. A reproduced audio signal which is thus obtained is produced according to a signal shown at FIG. 5(j) during a period between points of time t8 and t9 (or between t3 and t6). Meanwhile, the other head 4 likewise performs a reproducing action at a phase difference of 180 degrees from the above-stated reproducing action of the head 3 to give a continuous reproduced audio signal. For each of other areas CH3 to CH6, the signal PG(a) is phase shifted to a degree of n.times.36.degree. and recording and reproduction are performed according to the phase shifted signal PG(a) in the same manner as the operations mentioned above. These operations can be accomplished independently of the travelling direction of the tape.
The conventional audio dedicated recording/reproducing apparatus of the kind described is arranged to have many parallel channels. However, this causes the operator a great difficulty in locating recorded or unrecorded parts within each channel on the tape and in avoiding erroneous erasing, etc. In one conceivable method for solving this problem, information on these locations is arranged as additional data and is written into each channel together with PCM audio data. This method, however, requires reproduction of all tracks of all the areas for grasping the recorded condition of the tape and thus takes an extremely long period of time. Further, in preventing a recorded signal from being eroneously erased, the whole track portion of data must be taken in; any error is corrected; the additional data is alone rewritten; again an error correction code is added; and the data after these processes again must be recorded. To meet these requirements, the apparatus must have extremely complex structural arrangement.
Further, in extracting digital recorded data, it is a general practice to extract a bit clock signal used in writing the data and to extract the data by sampling data read out according to the clock signal. As regards the arrangement for extracting the bit clock signal, there is provided a preamble part for bit clock synchronization in front of the data area; and a clock signal which is oscillated by means of a PLL or the like and is synchronized with the clock signal written in this preamble part is employed as the bit clock signal. The conventional method thus necessitates the provision of the preamble part in front of the data to be written in. This deteriorates the efficiency in terms of data recording density. The data recording density, however, must not be lowered particularly in the case where some data relative to the recording condition much be recorded in each of the divided areas as mentioned in the foregoing. Besides, the conventional method requires the use of a bit clock signal extraction circuit, etc. which results in increasing the scale of the circuit arrangement. Further, since it is desirable to adopt a recording data self-clocking arrangement for controlling and monitoring the bit clock signal in extracting the data, the method lowers a degree of latitude in carrying out digital modulation for recording and the density of data recording.